1. Field of the Invention
The present invention relates to a semiconductor device comprising a pellet mounted on a radiation plate, the pellet and the radiation plate being resin-sealed together and a method of manufacturing the same.
2. Description of the Related Art
Semiconductor devices such as LSI (Large Scale Integrated Circuit) or MMI (Micro Monolithic Integrated Circuit) have heretofore been used in various kinds of electronic apparatus. For example, in a portable telephone, a semiconductor device which consumes a large quantity of electric power, such as an amplifier for the transmission/reception signal, is mounted in a micro cell.
Generally, the larger the power consumption of a semiconductor device is, the higher the temperature when the device is heated. Since the device life becomes short when the temperature in use is high, a semiconductor device which generates a remarkable amount of heat is equipped with a radiation plate. The radiation plate becomes more effective with a larger surface area, but in small devices such as a portable telephone, it is difficult to provide a large radiation plate in the semiconductor device.
Accordingly, in a general semiconductor device, for the purpose of preventing an excessive temperature rise of the device, how to effectively radiate the heat for maintaining the temperature in use at a low level becomes an important problem. In a semiconductor device like this, a pellet of a semiconductor device is mounted on the radiation plate. Electrode pads of the pellet are connected to lead terminals arrayed on its circumference by means of bonding wires, and the bonding wires, the inner part of the lead terminals and the pellet are sealed with a resin member.
Since the outer part of the lead terminal is projected outside from the resin member, when the semiconductor device is mounted on a circuit substrate and the lead terminals are connected to signal lines of the circuit substrate, it becomes possible to input various signals into the pellet or output from the pellet. Further, since the lower surface and the end portion of the radiation plate are exposed outside of the resin member, by connecting these portions to a conductor pattern of the circuit substrate, the generated heat in the pellet can be radiated to the conductor pattern of the circuit substrate through the radiation plate.
However, there is a possibility that the conductor pattern of the circuit substrate may become hot according to circumstances, and under these circumstances, it is difficult to radiate the generated heat in the pellet satisfactorily to the conductor pattern.
On the other hand, there is a semiconductor device in which a portion of the radiation plate is exposed to the upper surface of the resin member to radiate the generated heat in the pellet to the open air by means of the radiation plate. However, the method of radiating the heat to the open air is less effective compared with the method in which the heat is radiated to the conductor pattern as above described, and a good radiative property can not be expected if the temperature of the open air surrounding the semiconductor device is high.
Further, with the structure in which a flat radiation plate having the pellet mounted on its upper surface is exposed to the lower surface of the resin member, there is a fear that the radiation plate may fall off the resin member if no protective means is added. Therefore, in the prior method, the side of the radiation plate is bent into a form of a crank and set inside the resin member to prevent the falling of the plate. However, the provision of a part for the exclusive use of fixing the radiation plate to the resin member is unpreferable because it will decrease the productivity of the semiconductor device.